00:01
Here we're going to do an example of conservation of momentum.
00:05
So a reminder that momentum is conserved if there are no external forces acting on a system.
00:19
An alternative way of saying this is that if there are external forces, they are negligible compared to the interactions between the objects in the system.
00:38
And typically you have conservation of momentum with interacting objects, which interact via newton's third law pairs.
00:57
That is, two things collide, and the force that one object exerts on another is equal and opposite to the other's force exerted on it.
01:11
So a very typical situation is with collisions.
01:18
Even if there's friction in the road, when two cars collide, the collision forces are so large compared to that friction that you can basically neglect the friction.
01:30
So here's our interaction.
01:32
We have two birds.
01:34
One is a big hawk flying very quickly.
01:39
Let's see, we'll call him mass 1.
01:41
1 .8 kilogram, flying at a velocity of 28 meters per second.
01:52
Very fast for a bird.
01:55
And he catches up to a little tiny dove, which we'll call mass two.
02:06
That looks more like a bullet, but it's a tiny dove.
02:11
Has a mass of 0 .650 kilograms and is trying desperately to escape with 7 meters of a second velocity.
02:25
Okay, so we are going to conserve momentum.
02:29
What is momentum? momentum is a vector product of mass times velocity...